Betula humilis Schrank

Found over a wide geographical range, from Germany to eastern Siberia and Korea, Betula humilis forms a reasonably tall shrub, with thin twigs, minuscule buds and small, elegant, coarsely toothed leaves that often look as if they have been cut out with pinking shears. It is closely related to Betula fruticosa, with which it is united by some authors, though it is treated separately by McAllister and Ashburner (2013), which the present treatment follows. In B. fruticosa the leaves are more finely toothed, more tapered towards the apex and have more (5–6) pairs of veins. Particularly characteristic of B. humilis are the numerous translucent glands on the shoots which become white with age and persist on second year and older twigs (these are also seen in the tetraploid variant of B. fruticosa and in B. microphylla, probably indicating the presence of the B. humilis genome in the parentage of those species).

Betula humilis was described from Bavaria, at the western limit of its distribution, by the Bavarian Jesuit Franz von Paula von Schrank (1747–1835), director of the newly instituted Botanic Garden in Munich, and author – among other things – of the wonderfully illustrated Flora Monacensis (1811–1820). The species is rare in western Europe, recorded in a few localities in Germany south of Munich and further north in eastern Germany, and equally scarce further east in Poland, though reportedly more widespread in Russia (Jalas & Suominen 1976). It appears formerly to have been rather more widespread, its current range reflecting the effect of encroachment and human land use – both directly, through the gradual advance of cultivation and drainage, and indirectly, through competition from Salix species which respond more positively to eutrophication (the species’ confinement to wet soils in the wild may indicate low competitive ability in more fertile conditions).

In cultivation, Betula humilis grows successfully in even quite dry garden conditions in normal soil, and seems to be more shade tolerant than most birches, though it will not make an attractive plant except in good light. While not vigorous in cultivation, it is very persistent, even in competition with grass and other shrubs.